The use of circuit breakers is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems toward providing protection against over-current conditions. Various circuit breaker mechanisms have evolved and have been perfected over time on the basis of application-specific factors such as current capacity, response time, and the type of reset (manual or remote) function desired of the breaker.
One type of circuit breaker mechanism employs a thermo-magnetic tripping device to "trip" a latch in response to a specific range of over-current conditions. The tripping action is caused by a significant deflection in a bi-metal or thermostat-metal element which responds to changes in temperature due to resistance heating caused by flow of the circuit's electric current through the element. The thermostat metal element is typically in the form of a blade and operates in conjunction with a latch so that blade deflection releases the latch after a time delay corresponding to a predetermined over-current threshold in order to "break" the current circuit associated therewith.
Another type of circuit interruption arrangement, useful for interrupting circuits having higher current-carrying capacities, uses current transformers to induce a current corresponding to the current in the circuit path, and an electronic circuit monitoring this induced current to detect power faults in the circuit path. In response to a power fault being detected, the electronic circuit generates a control signal which actuates a solenoid (or equivalent device) to cause the circuit-interrupting contacts to separate and interrupt the circuit path.
Causing the circuit-interrupting contacts to separate, however, can be a problem. For instance, it requires a significant accumulation of energy which is typically scarce in such arrangements which are self-powered, and an unsuccessful attempt to interrupt the circuit path depletes the reservoir of accumulated energy. This problem has been addressed by using an undervoltage circuit which ensures that a trip is not initiated until the power supply has sufficient energy, and a power supply regulation circuit which keeps the voltage applied to the electronic circuit within pre-determined limits.
There are certain disadvantages to known circuit arrangements addressing these problems. For example, including both an undervoltage circuit and a power supply regulation circuit requires a significant number of components for proper control of the respective functions provided. Moreover, with two separate circuits, the maximum undervoltage level must be below the minimum regulated power supply level. This situation forces the power supply levels to be larger, which requires larger current transformers to support the extra power supply burden. In accordance with the present invention, it has been determined that these undervoltage and supply-regulation functions can be combined to reduce the power supply levels and eliminate the tolerance of the undervoltage circuit. Also the size of the current transformers feeding the circuit can be reduced because of the decreased voltage burden on them.
Accordingly, there is a need for a circuit interruption arrangement without the aforementioned shortcomings.